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<H1>Homebrew software defined radio</H1>
<P><FONT face=Tahoma><STRONG>VK3YE</STRONG> has made available a video showing a
demonstration of his homebrew software defined radio.</FONT></P>
<P><FONT face=Tahoma>The YouTube description reads:</FONT></P>
<P><FONT face=Tahoma>Testing a very basic software defined radio on the 80 and
40 metre amateur bands.</FONT></P>
<P><FONT face=Tahoma>Uses the easy to use SDRadio software developed by
<STRONG>I2PHD</STRONG> (see </FONT><A href="http://www.sdradio.org/"
target=_blank><FONT face=Tahoma>http://www.sdradio.org/</FONT></A><FONT
face=Tahoma>) and a simple hardware interface which is a direct conversion
receiver without audio filter or amplifier stages.</FONT></P>
<P><FONT face=Tahoma>Apart from an RF amplifier (not really necessary) all the
receiver's gain comes from the computer (microphone in used, not Line
in).</FONT></P>
<P><FONT face=Tahoma>This is a very 'bare bones' implementation for use with a
low-end laptop with a mono soundcard input. Unlike a 'proper' SDR there is no
image rejection. Hence signals will appear twice on the spectrum display (one
USB and the other LSB) and some juggling may be required to dodge interference.
Also signal to noise ratio will never be as good as a single-signal
receiver.</FONT></P>
<P><FONT face=Tahoma>The hardware unit comprises of (i) transistor VFO (using
ceramic resonators for 3.58 MHz (80m) and 7.2 MHz (40m), (ii) buffer stage,
(iii) single balanced diode product detector and (iv) transistor RF amplifier
(optional). Your favourite direct conversion receiver circuit without audio
filtering or amplification would work fine.</FONT></P>
<P><FONT face=Tahoma>This unit is USB powered but a 9 volt battery would also be
OK if you want to keep it independent from the computer (this also helps reduce
interference radiated from the computer).</FONT></P>
<P><FONT face=Tahoma>Performance isn't as good as a home station rig but in some
aspects is better than a basic direct conversion receiver. The AGC is a bit slow
for my liking and it would be good to have an option to switch it
off.</FONT></P>
<P><FONT face=Tahoma>There is a slight delay between when you adjust a setting
and when the resultant audio is produced. A weak signal is generally clearer and
less noisy on the commercial rig as well. And tuning can be fiddly when trying
to null out an interfering signal on the opposite image (a full SDR with stereo
sound card would fix this).</FONT></P>
<P><FONT face=Tahoma>Nevertheless for its simplicity this is an amazing receiver
and would be a good beginners project.</FONT></P>
<P><FONT face=Tahoma>Watch <EM>Homebrew software defined radio - a demonstration
: </EM></FONT><FONT face=Tahoma><EM><A
href="http://www.youtube.com/watch?v=mfdgxZPc2BI">http://www.youtube.com/watch?v=mfdgxZPc2BI</A></EM></FONT></P>
<P><FONT face=Tahoma>Soft Radio Yahoo Group<BR></FONT><A
href="http://groups.yahoo.com/group/soft_radio/" target=_blank><FONT
face=Tahoma>http://groups.yahoo.com/group/soft_radio/</FONT></A></P>
<P><FONT face=Tahoma>Soft Rock 40 Yahoo Group<BR></FONT><A
href="http://groups.yahoo.com/group/softrock40/" target=_blank><FONT
face=Tahoma>http://groups.yahoo.com/group/softrock40/</FONT></A></P></BODY></HTML>